A dual view Catadioptric Endoscope for fluorescence endoscopy

Fluorescence endoscopy has been identified as a potential diagnostic tool for early cancer screening thanks to the difference between fluorescence emissions of the malignant and normal tissue [1]. White light imaging based endoscopy is widely available on the market today, but only a handful has fluorescence imaging capabilities. Fluorescence endoscopy is a useful supplement to white light endoscopy since it could act as markers for automated screening of lengthy endoscopic video especially in the case of capsule endoscopy [2]. The autofluorescence emission signals resulting from endogenous tissue such as collagen and NADH in the GI tract are very weak [3], while most endoscopes only image forward view with low fluorescence light collection efficiency. The goal of this work is to investigate the feasibility of a wide field approach using catadioptric optics for autofluorescence endoscopy. Catadioptric optics involves the use of reflective and refractive optical components, such as mirrors and lenses. Catadioptric wide field imaging may be able to provide wide coverage of the field of view, decent light collection, as well as possible digitally reconstructed low distortion images using unwrapping algorithms specific to mirror geometries [4]. The catadioptric optical system would have custom optics that focuses two separate views onto the same imaging plane. The views would occupy separate regions on the imaging plane. The forward view is oriented along the endoscope's axis of symmetry, while the side view is a panorama oriented in the radial direction relative to the axis of symmetry. Each view is modeled in OSLO and custom lenses were designed to complement the mirrors. A 1:1 prototype includes one set of lens and mirror design that would fit inside a capsule endoscope of length 26mm and diameter 10 mm. The lens design solution is based on existing lens material and within current micro optics fabrication tolerances. The imaging plane is constrained to be within common CCD sensor sizes of 1/3” or smaller. The geometric RMS spot size is around 6 $\mu{\rm m}$. The prototype has minor magnification modification so that the imaging area would fit on a common CCD sensor size such as 1/3”.